1. Field of the Invention
This invention relates to a prosthetic ligamentary device.
2. Description of the Prior Art
From an anatomical point of view, it is desirable for an artificial ligament, during extension, to have elasticity followed by ridigity.
A prosthetic ligamentary device has been suggested consisting of a relatively inelastic cord attached at one end to one end of a helical tension spring. In its application to a knee joint, the cord is anchored at its other end to the tibia and extends at its one end into a hole drilled through the condyle of the femur and the other end of the spring is anchored to the femur outside the hole.
In use of the joint, the one end of the cord must move longitudinally in the hole, but this is disadvantageous, because the one end of the cord should preferably be immobile in the hole, particularly to allow growth of natural material into the cord if the latter is foraminous.
U.S. Pat. No. 4255820 discloses an artificial ligament which is tubular in overall configuration with flared ends, which have a graduated pore density to permit controlled hard and soft tissue ingrowth, and a central portion which prevents tissue ingrowth. The central section of the ligament is formed so as to be elastic along its longitudinal axis to permit the needed elasticity in use, having an elongation factor of between 4 to 6% of its length. Inserted within the central section is a cylindrical core of DACRON (a polyester formed by reaction between terephthalic acid and ethylene glycol), or cross-linked or vulcanized rubber, or high-density polyethylene. The core is effective to maintain the tubular shape of the ligament and to provide strain relief throughout the central section.